1. Field of the Invention
This document relates to a solar cell, and more particularly, to dyes for a dye-sensitized solar cell.
2. Discussion of the Related Art
In order to solve the critical energy problem, a variety of researches for replacing the existing fossil fuels are recently being done. In particular, in order to replace petroleum resources that will become exhausted in several tens of years, a variety of researches for using natural energy, such as wind force, atomic energy, and solar power, are being done.
From among them, a solar cell is environmentally friendly because it is based on the unlimited resources, the sun, unlike other energy resources. The solar cell has recently been in the spotlight owing to the recent worldwide energy crisis since the development of a silicon (Si) solar cell in 1983.
In this silicon solar cell, however, there is a cutthroat competition among countries because of the supply and demand of Si raw materials, and the cost of production is high. In order to solve this problem, many local and overseas research institutions propose solutions. One of the solutions which can solve the critical energy crisis is a dye-sensitized solar cell. The dye-sensitized solar cell has been in the spotlight by the academic world since it was developed by a research team (lead by Dr. Micheal Graetzel) of the EPFL (Ecole Polytechnique Federale de Lausanne, in Switzerland) in 1991. Active researches have been done on the dye-sensitized solar cell in many research institutions.
The dye-sensitized solar cell is a photoelectrochemical solar cell, generally comprising photosensitive dye molecules capable of generating electron-hole pair by absorbing a visible ray and transition metal oxides capable of transferring the created electrons, unlike in the silicon solar cell. From among conventional dye-sensitized solar cells, a dye-sensitized solar cell using nano-particle titanium oxides has been chiefly researched and developed.
The dye-sensitized solar cell using nano-particle titanium oxides is advantageous in that it can be fabricated cheaply when compared with the existing silicon solar cell and can be applied to glass windows in the outer walls of a building or a glass greenhouse because of transparent electrodes, but is disadvantageous in that it has low photoelectric conversion efficiency. Accordingly, the dye-sensitized solar cell using nano-particle titanium oxides requires more researches.
The photoelectric conversion efficiency of a solar cell is proportional to the number of electrons generated by the absorption of sunlight. In order to increase the efficiency, the number of electrons generated and the amount of sunlight absorbed need to be increased by increasing the amount of dyes adsorbed by titanium oxide nano-particles, and generated excited electrons needs to be prevented from being extinguished through electron-hole recombination.
There are several methods, for example, a method of fabricating the particles of oxide semiconductors having a nano-meter size in order to increase the amount of dyes absorbed per unit area, a method of increasing the reflectance of a platinum electrode in order to increase the amount of sunlight absorbed, and a method of mixing semiconductor oxide light scattering agents of a several micrometer size.
However, the conventional methods have reached the limit on improving the photoelectric conversion efficiency of a solar cell. Accordingly, there is an urgent need for the development of a new technology for improving the efficiency.